In general, a digital camera electrically records two dimensional (2D) information about an object. The digital camera converts an optical image of the object into an electrical signal and stores the electrical signal in a memory.
The digital camera can use an image sensor circuit to convert an optical image into an electrical signal. The image sensor circuit conventionally can be based on a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) image sensor circuit.
Light sources used by the image sensor circuit are mainly classified into sunlight and artificial light. A frequency of an alternating current (ac) power source used for artificial light, such as fluorescent lamp, differs by countries, but most countries use 50 Hz or 60 Hz.
The image sensor circuit includes a pixel array for capturing an image. The pixel array includes unit pixels arranged in rows and columns. When the unit pixels are exposed to light to capture an image, not all pixels may be exposed simultaneously due to concern over leakage current. Therefore, the image sensor circuit can sequentially be exposed on a row-by-row basis.
When an exposure time per row of an image sensor circuit is not an integer multiple of a period of a power used for a light source, flicker may occur in an output image. For example, when an image is captured at 60 Hz under lighting of a fluorescent lamp driven by a power having a frequency of 50 Hz, the light intensities reflected from the object may be different from row to row.
Conventionally, to remove flicker noise, the exposure time can be set to be an integer multiple of the period of the light source. However, because the frequency of the power source may differ by country, it may be inconvenient for the user to set the exposure time according to the frequency of the light source.
In addition, when the exposure time should be less than the period of the light source (e.g., when the light source is very bright), the exposure time may not be configured as an integer multiple of the period of the light source.